A new copper mine is to be started$-$up$.$ A $60$m wide orebody outcrops on surface and dips at

$85$ degree towards the south. The orebody is economic up to $200$m below surface. From

$200$m further deep the grades are very poor. Open pit has a limit of $150$m$.$ below that an

underground mine has to take over. Underground equipment will include LHD$$s$,$ drill rigs,

some of which are at most $4$m wide and $5$m high. A representative log of the host rock is

shown.

Given that:

$3$ joints sets are prevalent this environment. The joints are mostly curved and slickensided, with some fine material infilling.

Joint sets Dip $($degrees$)$ Dip direction$($degrees$)$ Ave. Joint spacing

J$1781101$m

J$2603000\mathrm{.}6$m

J$370700\mathrm{.}3$m

$$ RQD $=60$

$$ The host rock is slightly moist and wet in some locations

$$ K ratio $=1\mathrm{.}6$

Standard safety factor for the mine is $1\mathrm{.}3$ as a matter of policy $($ be it dumps, slopes,

underground support, etc.$).$ A company has requested you to perform a geotechnical design

feasibility $.$PART B

Given that the cost of waste removal is R$30/$m$3,$ ore material sells at R$1000/$ton$.$ Determine

the percentage gain in the open pit as a result of increasing overall slope angle by $1$ degreety.